PROJECT SUMMARY The increased incidence of Ductal Carcinoma In Situ (DCIS) and effect of high fat diet (HFD) and obesity on breast cancer malignancy are becoming formidable clinical challenges in treating and preventing this disease. Existing evidence indicates that only 40% of diagnosed DCIS, the most common form of non-invasive breast cancers, will eventually progress to invasive ductal carcinoma (IDC) if left untreated. However, due to an insufficient understanding of the underlying molecular mechanisms of invasive progression, there is at present no clinically useful way of predicting which DCIS will progress to become invasive. This has led to growing concern of DCIS over treatment leading to increased patient morbidity. Therefore, there is a critical need to find therapeutic and intervention strategies to prevent breast cancer progression in those DCIS patients at high risk for breast cancer. In human primary samples and in vitro cell line models, we have shown that Singleminded- 2s (SIM2s), a member of the bHLH/PAS family of transcription factors, is a tumor suppressor down-regulated in transition from DCIS to IDC by inhibiting epithelial mesenchymal transition (EMT) and metastasis. Our recent preliminary data show SIM2s down-regulation by saturated fatty acids is dependent on NF-kB repression of the SIM2 promoter by DNA methylation, and is blocked by dietary omega-3 fatty acids (FA). Based on our preliminary data that a high fat diet down-regulates and methylates the SIM2s promoter, we hypothesize that dietary-dependent prevention of SIM2s down-regulation by omega-3 FA will block DCIS progression. To address this hypothesis we propose two Specific Aims. In Aim 1, we will investigate the role of SIM2s in DCIS progression in response to HFD and intervention with omega-3 FA using Sim2+/- mice and a novel in vivo mouse intraductal model. In Aim 2, we will define the mechanisms involved in transcription and epigenetic regulation of SIM2 in DCIS progression. These studies will investigate the effects of HFD and omega-3 FA and epigenetic factors on the SIM2 promoter at different stages of disease and examine their efficacy for possible DCIS intervention. Once completed, we anticipate that this research project will provide a fundamental understanding of the link of SIM2s expression, type of dietary fatty acids and epigenetic reprogramming on DCIS progression.